1. Technical Field of the Invention
The present invention relates to a method of calculating power generating torque of a synchronous generator, especially, a vehicular Lundell-type synchrounous generator.
2. Description of the Related Art
In recent years, attempts have heretofore been made to reduce the amount of fuel, such as gasoline, to be injected into an engine with a view to achieving the improvement in fuel consumption. To this end, the engine is controlled in a pinpoint precision to rotate in stability. In the meanwhile, an electric energy needed for the engine for safety and comfort purposes is rising year to year and a generator (alternator), connected to the engine, has been increasing in size. This results in an issue with the occurrence of an increase in torque of the generator accompanied by instable rotation of the engine. For instance, under circumstances where large electric load is turned on to rapidly increase the electric energy of the generator, a drop occurs in a rotational speed of the engine with a consequence of engine stop.
To address such an issue, research and development work has heretofore been taken to provide technique of conducting integrated management of electrical loads through the use of a communication system inside the vehicle for predicting power generating torque to control the amount of fuel to be injected to the engine with a view to achieving stability in engine rotation.
However, even if the related art practice has enabled the prediction of the amount of generated electric power (electric current in generated electric power), a difficulty has been encountered in accurately calculating power generating torque on this occasion. Power generation torque represents a turning force equivalent to energy to be consumed. In this case, energy to be consumed is a sum of generated electric power and the amount of loss dissipated in heat. For example, even with output currents at the same value, variation takes place in a coil resistance value depending on surrounding temperatures with the resultant change in heating value. Thus, a need arises for accurately obtaining the amount of losses of the generator depending on an operating status of the generator and usage environment thereof, otherwise no success can be expected in calculating power generating torque.
Further, the amount of losses of the generator is broken down into copper loss, rectification loss, excitation loss, iron loss and mechanical loss. Among these, iron loss particularly consumed in an iron core results from hysteresis loss and eddy-current loss in mixture and, hence, a calculation formula becomes complex with the resultant difficulty in identifying the cause of losses. This results in deterioration in precision of calculation results. Moreover, a remarkable increase occurs in a time interval needed for calculation and it has been conceived that no computation of such factors is possible with a computer Installed on the vehicle.
Therefore, attempts have taken to preliminarily assume the environment for the generator to be used and prepare a map covering a whole range of conceivable combinations of factors while actually measuring parameters such as temperatures or the like and retrieving target torque from the map. However, this results in a need for preparing torque data in a multidimensional approach in conformity to various statuses and, thus, considerable efforts are needed for measurements. This causes a remarkable increase in a volume of data with the resultant increase in a retrieving time interval and another issue arises in a difficulty of processing these data in an ECU. Moreover, a large number of sensors are needed for measuring input values of the parameters and cause an increase in production cost. Also, if the volume of data and the amount of inputs are restricted, then, another issue arises with a difficulty in obtaining high precision.